The method for fabricating an organic EL display panel is broadly divided into two types, depending on a way of forming an organic functional layer. One is forming a thin film, which is an organic functional layer, by vapor deposition, and the other is forming an organic functional layer by ink application.
The method of forming the organic functional layer by ink application significantly improves material-utilization efficiency, as compared to the vapor deposition method, and allows models of display panels to be readily switched during mass production simply by changing a program installed in manufacturing equipment.
An inkjet device is one of exemplary means for forming an organic functional layer by ink application. The device dispenses ink containing organic functional materials to a substrate to form an organic functional layer (e.g., see Patent Literature (PTL) 1).
The ink containing organic functional materials is applied to colored-light emitting regions arranged on the substrate. The colored-light emitting region as used herein refers to a region in which sub-pixels having one of red, blue, and green are aligned. For example, on a substrate of a display panel, at least three different colored-light emitting regions of three different colors are arranged parallel to one another along a specific direction. It should be noted that in a display panel, a set of the following sub-pixels may be referred to as a pixel: a sub-pixel being a unit which emits red light; a sub-pixel being a unit which emits green light; and a sub-pixel being a unit which emits blue light.
The colored-light emitting regions are partitioned sub-pixel by sub-pixel by banks (walls). Alternatively, the colored-light emitting regions may be arranged line by line, without being partitioned from one another. In the colored-light emitting regions partitioned sub-pixel by sub-pixel by banks, the banks define each sub-pixel, and an ink containing an organic functional material is supplied for each sub-pixel during the fabrication of a display panel (e.g., see PTL 2).
On the other hand, in the colored-light emitting regions arranged line by line where they are not partitioned sub-pixel by sub-pixel by banks, an ink containing an organic functional material is supplied for each line of colored-light emitting region formed of a plurality of sub-pixels (e.g., see PTL 3).
Future organic EL display panels are becoming smaller in size and higher in definition, and pitches between sub-pixels and between the colored-light emitting regions are becoming narrower. Due to narrow pitches between highly-detailed sub-pixels and between highly-detailed colored-light emitting regions, it is difficult to dispense ink to a region enclosed by banks using an inkjet device.
FIG. 12 is a plan view showing a way of forming an organic functional layer on a display substrate, using an inkjet device. An inkjet head 20 applies to a substrate 10 an ink containing a dye, which is one of organic functional materials, for each colored-light emitting region 12.
(1) The inkjet head 20 included in the inkjet device is placed at the top (or at the bottom) of the figure, along the long axis of colored-light emitting regions 12 each defined by line banks 11 on the substrate 10. Preferably, the inkjet head 20 is placed such that an alignment direction of nozzles 21 is perpendicular to the long axis of the colored-light emitting regions 12.
(2) The inkjet head 20 is moved in parallel relative to the long axis of the colored-light emitting regions 12.
(3) The nozzles 21 dispense inks to the colored-light emitting regions 12 to form an organic functional layer.
The way of moving the inkjet head 20 in parallel relative to the long axis of the colored-light emitting regions 12 in this manner may also be referred to as “applying ink from top to bottom” below.
However, as described above, amounts of the inks dispensed from the respective nozzles 21 included in the inkjet head 20 vary from one nozzle 21 to another. Thus, when applying the inks to the substrate 10 of the display from top to bottom, there occurs variations in amounts of the inks that are applied to the respective colored-light emitting regions 12.
The above is described specifically with reference to FIG. 13, for example. FIG. 13 illustrates the components illustrated in FIG. 12 in different conditions under the same circumstance.
As illustrated in FIG. 13, if the inkjet head 20 includes a nozzle 21a (a clogged nozzle) that does not dispense ink, an amount of ink applied to a cell 12a of one colored-light emitting region 12 is less than an amount of ink applied to a cell 12b of another colored-light emitting region 12. The variations in amount of ink among the colored-light emitting regions 12 can lead to variations in thickness of organic functional layer among the colored-light emitting regions 12. The variations in thickness of organic functional layer among the colored-light emitting regions 12 can further lead to variations in luminance among the colored-light emitting regions 12, resulting in what is known as “streaks” on the organic EL display panel.
A method illustrated in FIG. 14 is a way to solve the problem “streaks.” FIG. 14 is a plan view illustrating positional relationship between the inkjet head 20, the line banks 11, and the colored-light emitting regions 12.
(1) The inkjet head 20 which includes the plurality of nozzles 21 is disposed on a side of the substrate 10 along the long axis of the colored-light emitting regions 12.
(2) The inkjet head 20 is moved vertically relative to the long axis of the colored-light emitting regions 12.
(3) The nozzles 21 dispense inks containing organic functional materials to the colored-light emitting regions 12 to form organic functional layer.
The way of moving the inkjet head 20 vertically relative to the long axis of the colored-light emitting region 12 in this manner may also be referred to as “applying ink from side to side” below. Ink from a greater number of nozzles 21 is applied to the colored-light emitting region 12 when applying it from side to side than when applying it from top to bottom. When applying ink from side to side, there is little difference in terms of an amount of ink applied per colored-light emitting region 12 even if the inkjet head 20 includes the nozzle 21a which dispenses no ink and a nozzle 21b which dispenses a large amount of ink.
In order to form an organic functional layer that has a uniform thickness by the inkjet head 20 dispensing inks to the colored-light emitting regions from side to side, the line banks 11 are formed in line shapes. Forming the line banks 11 in line shapes allows an organic functional layer that has a uniform thickness to be formed even if the inkjet nozzles dispense inks having different volumes or if some of them dispense no ink.
Furthermore, PTL 4 discloses a honeycomb-shaped colored-light emitting region 12. FIG. 15 is a plan view of colored-light emitting regions 12 disclosed in PTL 4. The colored-light emitting regions 12 are defined by wavy line banks 11. The colored-light emitting regions 12 each include a plurality of circular cells 12a and gaps 13 between the circular cells 12a. 
When the method illustrated in FIG. 14 is used to apply inks to the colored-light emitting regions 12 on a substrate which have the structure of FIG. 15, the ink is applied to the center of each cell 12a. In this way, an area to which the ink is to be applied is increased, thereby increasing a margin for deviation of a nozzle, for example.